The present invention is directed to a novel composition of matter which is a type of interpenetrating polymer network. The present invention also relates to liquid and solid imaging compositions containing such polymer products and including the use of such compositions as photoresists and solder masks.
Interpenetrating polymer network (also known as IPN) systems are finding increasing uses in polymer product development. Such interpenetrating polymer network systems and developments are described by L. H. Sperling in "Interpenetrating Polymer Networks and Related Materials", Plenum Press, New York, 1981, in pages 21-56 of "Multicomponent Polymer Materials" ACS Adv. in Chem. No. 211, Edited by D. R. Paul and L. H. Sperling, ACS Books, Washington, D.C., 1986, and in pages 423-436 of "Comprehensive Polymer Science", Volume 6, "Polymer Reactions", Edited by G. C. Eastmond, A. Ledwith, S. Russo, and P. Sigwalt, Pergamon Press, Elmsford, N.Y., 1989. Interpenetrating polymer networks are defined in such publications as a polymer system comprising two or more constituent polymer networks that are polymerized and/or crosslinked in the immediate presence of one another. In effect, such a polymeric system comprises two or more network polymers that interpenetrate each other to some extent and which are not chemically bound but which are con-catenated such that they can not be separated unless chemical bonds are broken. Each constituent polymer network is characterized as an extensive three-dimensional polymer structure in which most chains are crosslinked at least twice to other chains so that the network structure has dimensions comparable with those of the macroscopic material. The constituent networks may be catenated, i.e., physically interlocked, and may also be subsequently chemically linked together to a limited extent. While the above definition describes an ideal structure, it is recognized that phase separation may limit actual molecular interpenetration. Thus the material sometimes may be described as having "interpenetrating phases" and/or "interpenetrating networks". If the synthesis or crosslinking of two or more of the constituent components is concurrent, the system may be designated a simultaneous interpenetrating network. If on the other hand, the synthesis and/or crosslinking are carried out separately, the system may be designated a sequential interpenetrating polymer network.
A polymer system comprising two or more constituent polymers in intimate contact, wherein at least one is crosslinked and at least one other is linear is designated a semi-interpenetrating polymer network. This type of polymer system is considered to be formed in cured photopolymerizable systems such as disclosed in Chapter 7 of "Imaging Processes and Materials-Neblette's Eighth Edition", Edited by J. M. Sturge, V. Walworth & A. Shepp, Van Nostrand Reinhold, New York, 1989. Such photopolymerizable systems typically have one or more linear polymers as a binding agent and at least one addition polymerizable monomeric component having two or more sites of terminal ethylenic unsaturation. Frequently the binding agent is a simple polymer blend, i.e., an intimate mixture of two or more polymers wherein there is no covalent chemical bonding between the different species of polymer chains. During imaging exposure, the monomeric component polymerizes and crosslinks to form a polymer network in which at least some of the polymeric binding agent is entrapped thereby photohardening or insolubilizing the exposed area.
Organic solvent swellable polymer networks, i.e., microgels, are known and their use in photosensitive compositions, particularly in photopolymerizable resists, is disclosed in U.S. Pat. No. 4,726,877. Microgel is a term originated in the paint industry and it includes crosslinked spherical polymer molecules of high molecular weight such as of the order of 10.sup.9 to 10.sup.10 with a particle size of 0.05 to 1 micron in diameter prepared by emulsion polymerization. Crosslinking renders these microgels insoluble but capable of swelling in strong solvent without destroying the crosslinked structure. U.S. Pat. No. 4,726,877 also discloses that the polymer components can be varied during polymerization to produce core and shell microgel with different interior and exterior composition. Unlike interpenetrating polymer networks, during preparation of core/shell microgels, the shell typically is grafted to the core network by covalent chemical bonding.
Linear polymers with polymeric arms are known and typically are prepared by copolymerizing a conventional monomer with a macromer. Macromers are defined by Kawakami in the "Encyclopedia of Polymer Science And Engineering", Vol. 9, pp. 195-204 (John Wiley & Sons, New York, 1987) to be polymers of molecular weight ranging from several hundred to tens of thousands, with a functional group at the end that can further polymerize, such as an ethylenic, an epoxy, a dicarboxylic acid, a diol or a diamino group. European Patent Publication No. 280,979 discloses the use of such a polymer as a binding agent in a photopolymerizable material suitable for producing printing forms or resist patterns. The polymer binder disclosed consists of a film-forming copolymer that has a two-phase morphology and an average molecular weight (weight average) of more than 10,000. The copolymer is produced using a macromer with an average molecular weight (weight average) of 1,000 to 100,000.
Although the physical and chemical properties of preformed interpenetrating polymer network systems and semi-interpenetrating polymer network systems are desirable in photosensitive products, the fact that after their formation they are not soluble or dispersible in conventional coating solvents markedly reduces their utility in photosensitive formulations. There is a need, which is not met by the current technology, to produce polymer binders which have crosslinked or network-like structure for use in coatable and conventionally processable photosensitive systems to produce tough, flexible, adherent or otherwise useful polymer products, and to improve their end-use performance.